This invention is generally directed to toner and developer compositions, and more specifically, the present invention is directed to toner compositions, including magnetic, single component, two component and colored toner compositions wherein a diblock copolymer is selected for wax component dispersion enhancement, and wherein improved jetting characteristics are enabled with toners containing diblock polymers as compared to toners with elastic (elastomeric) modifiers, such as triblock, multi-arm and branched copolymers, or certain graft copolymers. It has been determined that certain diblock copolymers enable more rapid toner jetting rates, and furthermore, improve the minimum fusing temperatures of wax containing toners. In embodiments of the present invention, the toner compositions can contain at least two polymer resins, and in embodiments from about 2 to about 10 polymers comprised, for example, of a first resin, a second crosslinked resin, a wax component, and a block copolymer compatibilizer component. In an embodiment of the present invention, the toner compositions are comprised of resin particles, especially crosslinked extruded polyester resin particles, pigment particles, a wax component, such as polypropylene wax, and a diblock copolymer compatibilizer. There are also provided in accordance with the present invention positively or negatively charged toner compositions comprised of resin particles, pigment particles, a wax component, such as polypropylene wax, and certain diblock copolymer compatibilizers, and charge enhancing additives. In addition, the present invention is directed to developer compositions comprised of the aforementioned toners, and carrier particles. Furthermore, in another embodiment of the present invention there are provided single component toner compositions comprised of resin particles, magnetic components, such as magnetites, a wax component, such as polypropylene wax, and a block copolymer compatibilizer. The toner and developer compositions of the present invention are useful in a number of known electrostatographic imaging and printing systems, especially those systems wherein a wax is present in the toner. The toner compositions of the present invention, in embodiments, possess a wide fusing latitude, for example, about 100.degree. C., which is the temperature range between the minimum fixing temperature of, for example, from about 100.degree. C. to about 170.degree. C. required for fixing toner particles on paper, and the hot offset temperature, for example, from about 180.degree. C. to about 250.degree. C., which is the temperature where molten toner adheres to the fuser roll. The toner compositions of the present invention also provide toner images with low surface energy and a low frictional coefficient, which properties enable the effective release of paper from the fuser roll and provide for a reduction in image smudging. Further, the developer compositions of the present invention possess stable electrical properties for extended time periods, and with these compositions, for example, there is no substantial change in the triboelectrical charging values. Also, with the toner compositions of the present invention, the wax, which enhances toner release from the fuser roll and increases fusing latitude, is retained therein and the loss of wax from the toner is eliminated or minimized; and moreover, the toner compositions of the present invention with stabilized wax domains are more easily processed by extrusion, and are more easily jetted which allows more rapid toner production and lower toner manufacturing costs. The control of wax concentration also enables the economy of direct recycling of toner fines obtained after particle size classification which would ordinarily be discarded as waste material. The dispersion stabilization of wax by diblock compatibilizers, described herein, decreases the minimum fusing and release temperature, thereby improving toner fusing latitude.
The following United States Patents are mentioned: 4,795,689 which discloses an electrostatic image developing toner comprising as essential constituents a nonlinear polymer, a low melting polymer, which is incompatible with the nonlinear polymer, a copolymer composed of a segment polymer, which is at least compatible with the nonlinear polymer, and a segment polymer, which is at least compatible with the low melting polymer, and a coloring agent, see the Abstract, and columns 3 to 10 for example; 4,557,991 which discloses a toner for the development of electrostatic images comprised of a certain binder resin, and a wax comprising a polyolefin, see the Abstract; also see columns 5 and 6 of this patent, and note the disclosure that the modified component shows an affinity to the binder and is high in compatibility with the binder, column 6, line 25; and as collateral interest 3,965,021.
Developer and toner compositions with certain waxes therein, which waxes can be selected as a component for the toners of the present invention, are known. For example, there are illustrated in U.K. Patent Publication 1,442,835, the disclosure of which is totally incorporated herein by reference, toner compositions containing resin particles, and polyalkylene compounds, such as polyethylene and polypropylene of a molecular weight of from about 1,500 to about 20,000, reference page 3, lines 97 to 119, which compositions prevent toner offsetting in electrostatic imaging processes. Additionally, the '835 publication discloses the addition of paraffin waxes together with, or without a metal salt of a fatty acid, reference page 2, lines 55 to 58. Also, in U.S. Pat. No. 4,997,739, there is illustrated a toner formulation including polypropylene wax (M.sub.w from about 200 to about 6,000) to improve hot offset. In addition, many patents disclose the use of metal salts of fatty acids for incorporation into toner compositions, such as U.S. Pat. No. 3,655,374. Also, it is known that the aforementioned toner compositions with metal salts of fatty acids can be selected for electrostatic imaging methods wherein blade cleaning of the photoreceptor is accomplished, reference U.S. Pat. No. 3,635,704, the disclosure of which is totally incorporated herein by reference. Additionally, there are illustrated in U.S. Pat. No. 3,983,045 three component developer compositions comprising toner particles, a friction reducing material, and a finely divided nonsmearable abrasive material, reference column 4, beginning at line 31. Examples of friction reducing materials include saturated or unsaturated, substituted or unsubstituted fatty acids preferably of from 8 to 35 carbon atoms, or metal salts of such fatty acids; fatty alcohols corresponding to said acids; mono and polyhydric alcohol esters of said acids and corresponding amides; polyethylene glycols and methoxy-polyethylene glycols; terephthalic acids; and the like, reference column 7, lines 13 to 43.
Described in U.S. Pat. No. 4,367,275 are methods of preventing offsetting of electrostatic images of the toner composition to the fuser roll, which toner subsequently offsets to supporting substrates such as papers wherein there are selected toner compositions containing specific external lubricants including various waxes, see column 5, lines 32 to 45. Also, U.S. Pat. Nos. 5,229,242, which illustrates toners with KRATON.RTM., and 4,814,253 are of interest.
There are various problems observed with the inclusion of polyolefin or other waxes in toners. For example, when a polypropylene wax is included in toner to enhance the release of toner from a hot fuser roll, or to improve the lubrication of fixed toner image it has been observed that the wax does not disperse well in the toner resin. As a result, free wax particles are released during the pulverizing/jetting, or micronization step in, for example, a fluid energy mill and the pulverization rate is lower. The poor dispersion of wax in the toner resin and, therefore, the loss of wax will then impair the release function it is designed for. Scratch marks, for example, on xerographic developed toner solid areas caused by stripper fingers were observed as a result of the poor release. Furthermore, the free wax remaining in the developer will build up on the detone roll present in the xerographic apparatus causing a hardware failure.
The aforementioned problems, and others can be eliminated, or minimized with the toner compositions and processes of the present invention in embodiments thereof. The release of wax particles is, for example, a result of poor wax dispersion during the toner mechanical blending step. The toner additives should be dispersed well in the primary toner resin for them to impart their specific functions to the toner and thus the developer. For some of the additives, such as waxes like polypropylene, VISCOL 550P.TM. that become a separate molten phase during melt mixing, the difference in viscosity between the wax and the resin can be orders of magnitude apart, thus causing difficulty in reducing the wax phase domain size. A more fundamental reason for poor dispersion is due to the inherent thermodynamic incompatibility between polymers. The Flory-Huggins interaction parameter between the resin and the wax is usually positive (repulsive) and large so that the interfacial energy remains very large in favor of phase separation into large domains to reduce interfacial area. Some degree of success has been obtained by mechanically blending the toner formulation in certain types of mixers, such as the known Banbury mixer, where the temperature of melt can be maintained at a low level and polymer viscosities are similar. However, it has been found difficult to generate an effective wax dispersion in compounding extruders where melt temperatures are typically higher. The inclusion of a compatibilizer of the present invention is designed to overcome the inherent incompatibility between different polymers, and, more specifically, between toner resin and wax, thus widening the processing temperature latitude and enabling the toner preparation in a large variety of equipment, for example an extruder. The improvement in thermodynamic compatibility will also provide for a more stable dispersion of secondary polymer phase, such as wax, in the host resin against gross phase separation over time. The use of commercially available dispersants like Kraton G-1726 or D-1118, which contain triblock copolymers and high molecular weight components do not assist the thermodynamic stability and do not act as rubbery regions in the toner bulk. The elastic regions tend to create ductile fracture points and thereby reduce the jetting rate, and therefore contribute to increased cost of powder processing.
The toners of the present invention are effectively jettable, it is believed, because the specific copolymers added as wax compatibilizers disperse wax into domains less than, for example, 2 microns without toughening the toner composite of wax, wax dispersant, charge control agent and colorant. Moreover, the specific copolymers of the present invention are friable powders which enable better mixing of the toner components by extrusion processes.
A number of specific advantages are associated with the invention of the present application in embodiments thereof, including improving the dispersion of toner resin particles, especially a mixture of resins and wax; improving the dispersion of wax in the toner, thus eliminating the undesirable release of wax from the toner in the form of free wax particles during the pulverizing operation of the toner manufacturing process and the subsequent contamination of xerographic machine subsystems by free wax particles; avoiding pulverizing rate reduction resulting from the poor wax dispersion; maintaining the intended concentration of wax in the toner to provide enhanced release of toner images from the fuser roll and the avoidance of the undesirable scratch marks caused by the stripper fingers required for paper management; wide process latitudes during the mechanical blending operation of the toner manufacturing process; and effective mechanical blending of toner can be accomplished in a number of devices, including an extruder.
Illustrated in U.S. Pat. No. 5,229,242, the disclosure of which is totally incorporated herein by reference, are toner compositions comprised of resin particles, pigment particles inclusive of magnetites, waxes, and, for example, certain compatibilizers. More specifically, this patent discloses toner compositions comprised of first resin particles, second crosslinked resin particles, pigment particles, low molecular weight waxes, such as polyethylene, and polypropylene, such as those available from Sanyo Chemicals of Japan as VISCOL 550P.TM. and VISCOL 660P.TM., and the like, and as a compatibilizer a block or graft copolymer. Examples of compatibilizers illustrated in this patent include block or graft copolymers of the structures A-(block)-B, A-b-B-b-A or A-(graft)-B with the polymeric segments A and B each being compatible with a different polymer thereby permitting the compatibilizer to serve, for example, as a macromolecular surfactant. Examples of compatibilizers include block copolymers, such as the KRATON.RTM. copolymers, available from Shell Chemical Company, and STEREON.RTM. copolymers, available from Firestone Tire and Rubber Company. For example, KRATON G1701X.RTM., a block copolymer of styreneethylene/propylene, KRATON G1726X.RTM., a block copolymer of styrene-ethylene/butylene-styrene, KRATON G1652.RTM., a block copolymer of styrene-ethylene/butylene-styrene, STEREON 730A.RTM., a block copolymer of styrene and butadiene, and the like are suitable for improving the wax dispersion in styrenic resins. With KRATON G1701X.RTM., the A segment could be the styrene block and the B segment could be an ethylene/propylene block. In embodiments of the invention of U.S. Pat. No. 5,229,242, there are provided toners wherein the compatibilizer is of the formulas A-b-B, A-b-B or A-g-B wherein A-b-B is a block copolymer of 2 segments, A and B, A-b-B-b-A is a block copolymer of 3-segments, A, B and A, and A-g-B is a graft copolymer of segments A and B, wherein the polymeric segment A is identical or compatible to one of the components present in the toner composition, that is the toner resin, whereas the polymeric segment B is identical or compatible with the other polymer component in the toner composition, that is, for example, the wax. Thus, in embodiments of the invention of U.S. Pat. No. 5,229,242, the aforementioned compatibilizer can be comprised of rigid units, such as styrene, with the polymeric segment B being comprised of flexible, rubber-like units, such as ethylene/propylene. The molecular weight of polymeric segment A can be from about 3,000 to about 100,000, and the molecular weight of polymeric segment B can be from about 5,000 to about 200,000. The compatibilizer is present in various effective amounts, such as, for example, from about 0.5 to about 9 percent, and preferably from about 1 to about 5 weight percent in embodiments.
Although the invention of U.S. Pat. No. 5,229,242 serves its intended purposes, improved wax compatibilizer compositions have been developed after extensive research and many failures. Toners with the diblocks of the present invention enable improved extruder mixing and processing, more rapid toner jetting rates, improved wax dispersions, and improved fusing properties at reduced cost. The wax compatibilizers of U.S. Pat. No. 5,229,242 may be considered thermoplastic elastomers, which indicates a material that at room temperature (25.degree. C.) can be stretched repeatedly at least twice its original length and upon immediate release of the stress will return with force to its original approximate length. Although the elastomeric materials in the U.S. Pat. No. 5,229,242 do compatibilize wax, these high-molecular weight materials may also impart toughness and poor processing characteristics, such as poor toner jettability to the toner composite. Moreover, the aforementioned commercially available elastomeric materials are often mixtures of diblock and triblock copolymers which can possess counterproductive properties in toner applications.
Further, the commercially available resins of U.S. Pat. No. 5,229,242, when present in the toner between 2 and 5 weight percent, can adversely affect toner fusing and toner jetting rates. The glass transition temperatures of the diblocks of the present invention are less than 60.degree. C. in embodiments, whereas those of the U.S. Pat. No. 5,229,242 are believed to be near 80.degree. C.; the number of blocks for the polymers of the present invention are two, whereas those of U.S. Pat. No. 5,229,242 are 3, in many instances; the composition of diblock copolymers are, for example, less than 40 weight percent and are preferably between 20 and 35 weight percent of butadiene or isoprene wherein the diene components are either totally or partly hydrogenated, whereas those of U.S. Pat. No. 5,229,242 are usually more than 50 weight percent butadiene which are then completely hydrogenated. Because of the difficulty hydrogenating polystyrene-block-low molecular weight polyisoprene copolymers, it is believed that there are no effective commercially available styrene-hydrogenated isoprene block copolymers. The unique material compositions of the instant invention illustrated herein contain, for example, less than 50 weight percent olefin or hydrogenated olefin component and, therefore, are not elastomers.
In embodiments of the present invention, there are provided toners wherein the compatibilizer is a diblock copolymer of the formula A-b-B wherein A-b-B is a block copolymer of 2 segments, and wherein the polymeric segment A is compatible with one of the polymer components present in the toner composition, that is the toner resin like a polyester resin, and the polymeric segment B is compatible with the other polymer component in the toner composition, that is, for example, the wax. Thus, in embodiments the aforementioned compatibilizer can be comprised of rigid units such as styrene with the polymeric segment B being comprised of soft semicrystalline like units such as isoprene/ethylene/propylene/isopentene/vinyl-2-methylbutene. It is the unique composition of the A-b-B diblock copolymer which enables the substantially permanent dispersion of wax into the toner composite into dimensions less than 2 microns. The molecular weight of polymeric segment A can be from about 3,000 to about 50,000 and preferably near 20,000, and the molecular weight of polymeric segment B can be from about 1,000 to about 30,000, and preferably between 10,000 and 20,000. The compatibilizer is present in various effective amounts, such as, for example, from about 0.5 to about 5, and preferably from about 1 to about 3 weight percent in embodiments.